The invention relates to a dial assembly enabling readings to be taken simultaneously on English and Metric scales of measurement and is adapted particularly for use with a machine tool wherein linear movement of the carriage, cross slide, tool, etc. is effected by means of a feed screw.
Characteristically, machine tools have indicator dials which are calibrated in either English or Metric units, depending on the standard of measurement used in the particular country. Several English-speaking countries, however, are presently in the process of changing from an English system to a Metric system, and since the conversion is being effected gradually, the manufacturing industry is often required to produce both products which conform to Metric specifications as well as those which conform to English specifications. Possible ways to provide this capability are to maintain two sets of machinery calibrated in English and in Metric units or to require operators to perform the necessary conversion calculation. Economic and time considerations, however, render these solutions inadequate and point up the advantages of modifying existing machinery to render it capable of indicating linear displacement in both English and Metric units.
In one type of prior art device, the English and Metric scales are carried by a single dial and clutch means are provided for bringing the conversion gearing into play whereby the reading may be made alternatively in English or Metric units. In another apparatus, English and Metric readings may be made simultaneously by means of internally toothed ring gears and a pinion gear in intermeshing engagement therewith. A disadvantage to using internally toothed gears, however, lies in the fact that they are more difficult and expensive to manufacture than externally toothed gears.